Objective: Catechol-O-methyltransferase (COMT) gene was hypothesized to have a relationship with human prefrontal cortex (PFC) function and individual cognitive abilities. The object of this study was to investigate the possible impact of genotypes of COMT Val<sup>158</sup>Met polymorphism on cognitive ability among children living in the Qinba region in China. Method: A total of 305 children were included, 163 girls and 142 boys; both complete IQ evaluation and Val<sup>158</sup>Met genotyping results were obtained. The quantitative traits of psychometric IQ were calculated by using the Chinese Wechsler Intelligence Scale for Children. All subjects’ genotypes of COMT gene Val<sup>158</sup>Met polymorphism were identified with the restriction fragment length polymorphism method. Results: The F test showed that the average scores (including the Full Scale IQ, Verbal Scale IQ, Performance Scale IQ and three index scores) did not significantly differ among different groups defined by Val<sup>158</sup>Met genotypes, neither in boys nor in the total group (p > 0.05). There was a significant difference between the average of Freedom from Distractibility score among different genotypes found in girls (p = 0.033). Conclusion: Our results indicate that COMT gene Val<sup>158</sup>Met polymorphism may be related to the intelligence of Chinese girls, although the results cannot withstand multiple testing. Consequently, further studies with larger samples and perfect design still need place more emphasis on the gender difference and compensation effect of dopamine activity in PFC.